Making Printing Cabinet with Dry Boxes - Some Questions  

Making Printing Cabinet with Dry Boxes - Some Questions

Note: Some of this applies to using an MMU (specifically the MMU3), but there's other questions that aren't about just that one piece of equipment, so I'm posting here. (Also, I've asked about this in some places, but not about the same issues.)

I live in a seriously humid area and I'm making a print cabinet so I can keep my filament dry. I'm rethinking my original design. My plan has been 2 compartments, a lower one for storage, then a row or two of drawers (for tools, supplies, parts, and so on), then, above that, at a level I can comfortably access when standing, is a 2'x4' (about 60x120cm) surface for the printers. Both the print compartment and the storage compartment would have their own powered dehumidifiers and I can easily add drains so I don't have to empty their water trays every day. The rows of drawers between them are not dry boxes. Both the print and storage dry boxes are independent.

Above the printers, in the print compartment, my design included printing hangers that would come down from the top and hold filaments spools, which would make it easy for the filaments to feed into the MMU and would provide a place for quick access to filaments I was using the most often. One reason for this is that, in my humid environment, using the MMU has been seriously frustrating. If the filaments are not dry enough, there are problems with the feeders in the MMU grinding down the filament instead of pushing it through and, often filament that's been in a humid setting, would break in the PTFE tubes and cause problems with the feed in the MMU. (And the control software doesn't allow for "accidents" so if something goes wrong, I have to power cycle my printer too I can deal with the mechanical issues.)

Yesterday, when I was doing maintenance on one of my printers, I realized I would often have the doors to the print compartment open for a while. I have to open them to remove prints from the printer, to clean the print bed, for maintenance and for feeding the filament into the printer. So I figure I can count on that compartment being open a decent amount. That would be a problem for the filament stored above the printers, since it's in the same compartment.

Also, one last detail: I have not started printing with ASA or ABS yet because I've heard about the smell issues and often need to be able to do other work in my workshop while I'm printing. So the compartment with the printers would be vented, as part of a vent system I've designed, so after a print, I could give it a few minutes to cool down, then turn on the fan and vent it to outdoors before I open it. (And I would have a valve or gate so the humid outdoor air does not come in through the vent.)

Also, I do have a filament drier that dries 2 spools at a time. But one thing I'm trying to cut down, with this cabinet, is the need to do extra things, like unload filament, cut it, then reload it (especially with the MMU), or having to dry a filament for 4-8 hours before using it. That kind of thing seriously upsets my workflow and thought process.

I'm thinking of redesigning for 3 dry boxes: Main storage (down below), Frequently Used storage (above), and printing (above, but below the Frequently Used. The dehumidifier I've been using successfully to dry out some other spaces has worked well and is not that expensive, so if I have to use 3 of them, that's not a major expense or burden. I can feed the filaments from the Frequently Used storage to the print compartment through grommets or something else to keep humidity from getting into the storage area. 

So this leaves questions and thoughts I'd like feedback on:
* The MMU3 is designed to mount on top of my frame for my MKS3.5+. Is there any real issue with moving it to inside the upper filament storage area? That'd put it about 8" farther from the printer, but I'd still be using PTFE tubes from the filaments to the MMU3, and from the MMU3 to the printer. That way the MMU3 is in a dry box that will be drier than the print compartment. 
* If I have a PTFE tube coming out of the upper storage area to the print head, will that do a good job of keeping the filament in it fairly dry? (I would think so, since the tube end goes right into the print head and leaves only a VERY small space for moisture to come in, and a lot of that is filled with the filament.)

My main concern is keeping the filament dry on the run from the storage box, through PTFE, into the MMU (and 2-3" of filament is exposed within the MMU), or into the print head without any issues.

I don't want to get into what materials to use, construction methods, or design details. I mainly want to get comments and thoughts on the issue of keeping filament from getting too saturated for the last few inches (or feet, if you include the MMU and cassette) of the trip to the printer.

(For reference, it's spring now where I live and inside the workshop, the hygrometers are reading about 35% humidity, which is close to average for outside this time of year. During the summer, outside can be 70% or more.)